Adjustable magnetron



3 Sheets-Sheet l ATTORNEY June 27, 1950 c. v. LITTON' ADJUSTABLE MAGNETRON Filed Nov. 1, 1945 W H %N 1 mm mm as ha m INVENTOR CHARLES 1/. urro/v June 27, 1950 c. v. LITTON 2,512,901

AAAAA EY C. V. LITTON June 27, 1950 Filed Nov. 1, 1945 Patented June 27, 1950 ADJUSTABLE MAGNETRON Charles v. Litton, Redwood City, Calif. Application November 1, 1945, Serial No. 626,130 I 18 Claims. (01. 25027.5)'

This invention relates to magnetrons and in particular to magnetrons of the plural cavity resonator type. More specifically the invention provides an improved mechanical structure whereby the operating frequency of the magnetron may be varied over a considerable range in a positive and reliable manner.

In their origin plural cavity magnetrons were of a fixed frequency type, i. e., they were constructed without the benefit of adjustable electrodes whereby the electrical constants of the cavities could be varied to change their'frequencies of operation. The theory of operation of cavity magnetrons is well known to those skilled in the art and the theory will not be repeated here except to note that the frequency of operation is determined by the electrical constants of the cavities, the latter usually being dimensioned so that they oscillate substantially at half wavelength lines.

More recently cavity magnetrons have been developed in which the electrical constants of the cavities may be changed thereby permitting the magnetrons to be operated over a range of frequencies. Change in frequency is preferably accomplished by moving a low loss conducting element relative to the region of electromagnetic field concentration in the half wave length resonant cavity. The counterelectromotive forces set up in the conducting element produce a field which is opposed to the original field thereby reducing the total field. The inductive property of the resonant cavity is thereby reduced and the frequency thereof is increased. Similarly, a sec-' ond conducting element may be positioned so that it may be moved relative to the region of electro-static field concentration, this region being near the open end of the cavity. When this second conducting element is positioned between the fixed ends of the cavity the electrostatic field is increased due to the increase in capacitance. This results in a reduced frequency.

Preferably, and in accordance with my invention, I so construct the two above mentioned conducting elements that they form a unitary all metallic structure, the two elements being positioned on a plurality of guide rods, the latter being journaled'in suitable bearings by which the rods may be moved relative to the cavity as will be clearly explained hereinafter. It is to be understood that each cavity of the magnetron has its own set of tuning elements and that all said tuning elements comprise the unitary tuning structure. Among the objects and features of my invention are means to provide:

1. An improved mechanical arrangement for adjusting the frequency to which a magnetron may be tuned.

2. An arrangement of guides for constraining the motion of the tuning elements of an adjustable magnetron.

3. A guide rod and bearing arrangement for the tuning elements of an adjustable magnetron which will not become misaligned when subjected:

to the heat of operation of the magnetron.

4. The above three enumerated objects in com-' bination with means for preventing the magne-' ity magnetron, the section being taken through,

What is essentially the axis of symmetry and showing the tuning elements mounted on their guiding structure and the mechanism for adjusting same to the desired position. The sectionalso shows the method of mounting the cathode of the magnetron and the means for extracting the high frequency energy from the resonating cavities.

Fig. 2 is a partial view looking toward the plane perpendicular to the axis of symmetry at the section 2-2 of Fig. 1. The figure shows essentially the construction and positioning of th capacitance varying elements or C-ring.

Fig. 3 is a partial sectional view looking toward the plane perpendicular to the axis of symmetry at the section 3-3 of Fig. 1. The figure shows the construction and positioning of the inductance varying elements or L-ring.

Fig. 4 is a partial sectional view showing the method of grounding the L-ring to the main body of the magnetron. The View is taken looking toward the plane of the section 44 of Fig. 1.

Referring to the figures the reference character I represents the body of the magnetron to which other parts are brazed or otherwise suitably fastened to form a structure capable of bemagnetron may be tuned as will be hereinafter de- I scribed. This adjusting mechanism does not constitute a part of my present invention anda the trace l7.

1 ing the latter.

1 suitable material.

detailed description will therefore not be given.

, However in general, a platform 5 is brazed to a Sylphon bellows 6 which is in turn brazed to a bearing holder 7, the latter being brazed to the housing 2 along the circumference B. When the magnetron is evacuated, the external atmospheric pressure tends to extend the bellows and force I the platform 5 inwardly. This tendency must be 1 constrained and a method for accomplishing same will now be described. A rod 9 is brazed to the platform '5 and extends through the bellows and the bearing holder.

A hardened and ground sleeve I0 is held in position over the rod by the tongue nut II and the lock nut- 12. tongues I3 fit into slots in the sleeve lll. 'When the nuts are tightened this prevents any relative motion between the rod and the sleeve. A bearing I4 is positioned over the sleeve [0 'andis The 4 required by connecting the power supply leads to the terminals 39, 4B, and 4 l ,these terminals being screwed onto threaded rings 42, 43, and 44 respectively. The rings are brazed to the metal cups 26, 21 and 28 thus insuring good electrical connections throughout.

The above described cathode support assembly is one of great rigidity. However, if still greater rigidity and freedom frompossible vibration is required-the rod Blmay be .-ext:ended and inserted into a bearing in an insulating support ring 45 which may be held within the pole piece ie-by welding a ring 4'! to the pole piece as shown.

The-pole-piece it is actually made in two parts 48 and 49 and held in alignment by the act as guides for'the tuning structure and toclamped against the bottom of the bearingiholder I by the inner ball race 15. The thrust bearing ball retainer withballs 1 6 and theouter-ballrace lTLare-held against the race by atmospheric pressure and the nut [3, the latter bearing'against the longitudinal motion of the platformi. .A control knob, 1 9 -is fastened to the nut If) for turni A scale .20 is provided on the outerndiameter of the "knob and is aligned adjacent a .fixed scale 2| on-anindicator ring 22, the-latter being clamped to the extension -2 as shown. .Ameasureof the longitudinal motion is I thus obtained.

On the aforementioned cylindrical extension 3 is mounted the cathode support assembly. Since this assembly is not part vof-my present invenapplication, Serial Number 626,132, entitled Cathode-Support and filedNovemberl, 1 945,

which is now United States .Patent 2,474,263,

issued- June 28,1949. It will only be brieflyde- 1 scribed here. vA support cup 23 .is brazed to the extension 3 and toa tubularsealing-member.24.

This member and the other .members which. are partofqthevmetal to glass seals for insulating the-cathodesupporting members one fromanother is preferably. -made of Kovar or other insulatingportionzZ 5fol1owed byaseries of three ablyof thoriated tungsten, .so mounted ar1d--.energized- .as r to constitute a :bifilar filament. In .a

bifilar. filament the current inwadjacent, turns flows in Opposite directions withthe result that.

the magnetic field-due --to the current .is substantially neutralized. .If alternating currentis employed to energize the filament :as i usually ciably. modulate .themagnetron output current.

Qneendof one filament is'connectedto asemicylindrical member -32 which is in turn fastened; to -a conical or -other conoidal shaped support 33,..thelatter :being brazed to the metal .cup 25.

Oneendof the other filament winding is connected in a similar manner through another semi-cylindricalsleeve member 34, andconical support 35 to --metal cup :21.

The other ends ofeach-filament are connected to a member 36 whichtin turn-is brazed to .arod the latter being .brazed'to the central support '38. ,Power for ?-energizing the cathode :may. be applied :as

Sealed to the member 24 is-an,

Relative rotation between :the nut I8 and .the sleeve 10 determines the extent .of

1 tion,.-but-isdescribed and claimed in a separate =gether with said tuning structure forms oneof the features of my invention. The pole piece 46 is firmly held in .place with' the .extension .2 by crimping the latter against .thewpole apiece at a plurality ofpoints- 52.

Similarly the pole piece -.53 .is divided into two parts 54 and =-5.5.-- Betweentheseipartsis positioned a second-.guide ringfifi also having a pinrality of guide holes .therein. Pole .piece 53 is held in-position within-the extension -3 by the support-mp2? aslshown. .The-twoguide rings 5! and 56 are not clamped between-their respective pole piecesbutare free to expand under the heat of .operation'of the'magnetron. This prevents any. binding action whichi mightiother- Wise occur. 7

I have illustrated my invention as .appliedto :a twelve cavity magnetron-although it may be-eapplied to a magnetron having any number of cavities or-to any tube-structure [or electron discharge-device requiring similarv operating features. Referring to Fig. 2, I have :shown :a View of the magnetron'looking toward a plane passing perpendicular through the axis-of symmetry and showing. the twelve'cavities and the C-ring .or capacitance' var'yingelement. The .twelve cavities are formed b brazingtarplurality of vanes 5l-around the inn-erwdiameter of .the body! as shown. Each; cavity constitutes in effect-a quarter wave line which, when resonating-has -a -magnetic flux concentration adjacent its shorted 60 1 thecase in practice-the small amount :of any. residual alternating flux is insufficient .to appreendy-the short-.being-the-inner--wall of the body I. ThiS'iiS the :regionof high current density-as is well known. -Betweeni'the inner surfaces of the *vanes zisthe region of maximum concentration-of ele'ctric flux, this being-pointer maximum alternating potential difference,

.Inworder to :change the resonant rfrequencyaof the magnetron l-two t'means -.are provided-, -one. an L-:ring :5 8' (shown in -Fig.'=.- 3) the other, a-O-rihg 59 -(shownin Fig. '2) The- L-ring;comprises :a

plurality of metal :or conducting elements. preferablyformed by-mi-lling out slots in arsolid metal piece whereby-a"unitary-structureis :obtained.

The -conducting :elements are io'f va size "such that they-mayfreelyenter: and egress.:the-cavitiesrin the regionofimagnetic 'flu-x concentration, ,.=As the :elements enter. this region. the iefiective' sinductance of the cavities is -decreased and the cavities become --resonant at a higher frequency.

The C-ring also comprises a, plurality-of con ducting elements .formed Ia manner similar to thatof the L-ring. The-dimensionsiand :size

of these elements, .however, are-such :that they. may freely enter -.-or egress the ,-cavities.in-:theregion of -maximu1nelectric :fluxwoncentration; r As the elements :of the "Caring-renter this reg-ion the effective capacitance of the. cavities isv increased and the cavities become resonant. at a lower frequency. Claims directed to my improved method of varying the effective capacitance of magnetron resonant cavities are contained in a separate application, Serial Number 626,131, en-

titled Reactance Tuning Device and filed November 1, 1945, which is now U. S. Patent No. 2,495,744, granted January 31, 1950.

In accordance with my invention the L-ring and the C-ring are mounted on a plurality of, metal guide rods 60 and 6| so that together with.

the latter a unitary metallic or conducting structure is formed. The L-ring and the G-ring are.

positioned in general on.opposite sides of the resonant cavities in a manner such that as one ring enters the cavities the other ring emerges therefrom. This provides a more uniform vari-' ation of frequency with respect to the rectilinear motion of the rings and also permits of a greater range of frequencies with a smaller motion.

As shown in Fig. 1, the guide rods 60 are somewhat longer than guide rods 61. The rods of the two groups alternate around the L-ring and c-ring structures. It will be seen that the longer rods 60 extend a considerable distance beyond both sides of ring structures and pass through and are journaled in the guide holes of the guide rings 5| and 56. The shorter rods 6| extend only to oneside of the C-ring structure and are journaled in only one. guide ring. On

the other side, the guide rods 6| are fastened into larger rods 62, the latter being fastened to both the L-ring 58 and the platform 5. Thus it will be seen that a motion of the platform is transmitted to the L-ring and C-ring structure whereby an adjustment or tuning of the cavities is accomplished. By employing a plurality of small guide rods and bearings arranged on a circle having a diameter relatively great with respect to the diameters of the rods, the tendency for the mechanism to bind is substantially elimi-' nated. 'It has also been found that the above described guiding arrangement as applied to the movable elements of a magnetron has resulted in a lesser tendency for the magnetron to operate parasitically or on undesired modes.

The guide rods 60 and 6! are preferably made of tungsten while the guide rings may be made of copper. It has been found that the combination of tungsten and copper makes a very good bearing which will stand up under the high temperatures and other conditions encountered in vacuum at high frequencies. This is the result of the fact that tungsten is a refractory metallic material and copper is a non-refractory metallic material; i. e. the former is especially resistant to the action of heat and the latter is not.

As a means for preventing the magnetron from oscillating on undesired modes, i. e., modes other than the one determined by the dimensions of the cavities, the L-ring is grounded directly to the main body of the magnetron by an even number of coiled springs 63 and 64 as shown in detail in Fig. 4, this figure being a view 44 taken through the plane of the springs as shown in Fig. 1. A groove 65 in the periphery of the L-ring has a depth such that in order for the turns of the springs to lie in the groove they must be compressed sidewise in echelon fashion as shown. A spring compressed in this manner is much more resilient than if it were compressed across its diameter with the result that the L-ring is uniformly grounded and yet may be easily moved relative the cavities with no tendency toward field coils of the magnetron'that a deflecting fieldbinding. By making the coiledgrounding springs;

equal in number (two being partially illustrated in Fig. 4) and so compressing them thatthe coils are inclined in opposite directions around the L-ring,.a1possible tendency for the springs to produce a rotational movement of the L-ring is obviated since all tangential forces are balanced: The grounding of the L-ring is effective in re-.: stricting the overall active dimensions of the L-ring and as above stated tends to prevent oscillations on undesired modes.

To further prevent undesired modes of oscillation a member 66 is fastened to the platform 5 in a manner such that a substantial capacitance exists between the member 66 and the grounded.

extension 2. At the high frequencies of operation the capacitance effectively short circuits the platform 5 to ground.

As is well known when the magnetron is in operation the instantaneous oscillating potentials on the adjacent vanes which form the cavities are equal and opposite. In other words the currents in adjacent cavities are of opposite. The current in alternate cavities are phase. therefore in like phase. To closely couple the alternate cavities together and to force them to oscillate in effect as a single cavity, the alternate vanes are fastened together in a known manner by straps 61 and 68 as shown in Figs. 1 and 2.

Oscillatory energy from the cavities of the magnetron is extracted for useful work by coupling a wave guide 69 to one of the cavities through an impedance transformer. former comprises a pair of ramps 19 positioned within a horn shaped member H. Adjacent the cavities the ramps are close together and. therefore of low impedance to substantially match the impedance of the cavities. The ramps diverge outwardly and as they approach the wave guide 69, their separation and the internal dimensions of the horn determines .their impedance which is designed to substantially match that of the wav guide.

Although the impedance transformer is ap parently coupled to only one cavity, the fact that alternate vanes are strapped together results in the transformer being actually closely coupled to all cavities which as aforesaid oscillate as a unit.

In order that the magnetron may be evacuated and still transmit wave energy from the impedance transformer into the wave guide an insulating window 12 is sealed over the outer end of the horn H. The window is preferably elliptical in shape and so dimensioned that at approximately the mean frequency to which the magnetron may be tuned it represents a substantially infinite impedance across the wave guide and therefore does not appreciably infiuence the operation of the magnetron.

It has been found that during magnetron oscillation there are occasions when free electrons apparently escape from the cavity of the magnetron to the space within the horn H. If these electrons strike the window with sufficient velocity, the window becomes heated and failure due to suck-in will occur. In order to prevent such failures, two magnetic shoes 13 and H are positioned one on each side of the horn H as shown in Fig. 1. The magnetic field which is essential to magnetron operation is produced by field coils 15 and 16 shown schematically in Fig. 1. The above mentioned magnetic shoes are so positioned with respect to the field poles and The transi which a coolant'fiows.

isiproduccd across sthe'shoessubstantially at right v 1 November 1, 1945, whichisnow United States Patent 2,477,633: issued August 2, 1949.

The elements of "the magnetron' which: carry the'oscillatory currentsmayi be madeoficopper if moderatepowers are to begenerated. However, greater powers may be generatedlby employing elements made of tungsten or other highly refractory metal. a

The magnetron is preferably liquid cooled and this has beemillus'trated lby the tubing ll through The control assembly 4' may also be liquid cooled-as shown by the inlet and outlet tubings .18 and =l9 respectively positioned in the central hollow portion of the rod 9.

Although I. have illustrated only a single embodiment .of .my invention other modifications is my intention that the scope of my invention be limitedonly .by the objects thereof and the guide .ring concentrically mounted .oneach pole piece, a plurality of guiderods journaled in said' guide rings, an L-ring and a C-ring fixedly mounted on said rods and having tuning portions positioned to enter into or egress rfrom :said resonators when said guiderodsaremoved longitudin'ally, and means connected between said body and said rods for producing said longitudinal motion to vary the tuning of said magnetron.

2. An adjustable magnetron in accordance with claim 11 wherein eachof said "pole pieces :are divided into two 'partsi'iand :said guide ring is mounted between said parts.

3. The adjustable magnetron of claim 1 wherein the mounting :of said guide rings on said pole pieces permitsfree radial 'motion of saidguide'. rings.

4. An adjustable magnetron accordingto claim 1 in combinationwith means for-grounding'at least one of'saidrings directly to'said body,-.said grounding means comprising a'coiledspring'positioned between said one of said :Iings andsaid body.

5. An adjustable magnetron according-to claim 1 in combination with means'for groundingat least one of said rings directly to said body, said means comprising an even number of coiled springs positioned between said .one of saidringsand said body, the turns :of said springs being compressedsidewise in-echelon fashion.

6. An electron discharge -device comprising. an envelope, a plurality of cavity resonators-' inside said envelope, means in said resonators in'the regions at which a strongelectromagnetic; field develops duIing -uperation-for varying the-frewillbe apparent .to one skilled in the art and it quency of said resonatorsca plurality of guiding elements :upon which saidirequency varying meansaretmo'unted;-ssaid guiding element bein mounted on Jsaidvenvelope on opposite sidesof saidresonators; and means between said envelopev and said guiding 'elements for constraining the 'motion of said guiding elements.

7. An-electrondischarge device according to claim 6 in which said frequency: varying means comprises a first plurality of metallic elements mountedlonsaidguidingmeans at positions adja- =centregionsiinsaid resonators atwhich a strong.

said cavity. resonators and a second plurality of metallic.-elements mounted on said guiding ele-' ments. at positionsadjacent regions in said resonators' at which-astrong concentration of magnetic .fiux develops during operation for varying the .efiective inductance of said cavity resonators.

8. :In combination, a cavityxresonator for sustaining. ultra high frequency :oscillations, said resonator-shaving a region in whichmagnetic flux concentrates during operation and a region in whicln'electricflux concentrates during operation, and means for varying the relative values of said concentrations comprising a movable unitary metallic: member passing between the sides of said resonator and mounted on opposite sides of said resonator, said. member having a portion mounted adjacent the region vof magnetic flux concentration andanother portion mounted adjacent the regionof electric flux concentration, said portions being adapted respectively to enter into and egress from said regions-simultaneously or vice versa.

9. An-electron discharge :device comprising an envelope, a plurality of cavity resonators inside said envelope, means in said resonators in the regions'at which a strong electromagnetic field develops during operat-ionfor'varying the frequency of-said'resonators;aplurality of guiding elements :upon which said frequency varying means: are mounted; said guiding elements being mounted in said envelope on opposite sides of said resonators, .vmeans mounted between said envelope and said: guiding elements vf or constraining the=motionof said 'guiding'elements, said last-mentioned means comprising two groups of elementsrhaving bearing surfaces.

10. An electron discharge device according to claim 9 in which said'frequency varying :means' comprises a plurality of metallic elements mounted on 'said guiding elements at positions adjacent regions .in said; resonators at which a strong concentration :of electric flux develops duringoperation.

11. An adjustable magnetron comprisinga supporting bo'dyyaplurality of vanes mounted inside said-body integrally therewith, the size and position of said-vanes forming together With said body :a plurality of cavity resonators and determining substantially ;a mean frequency to which thermagnetron maybe tuned, a guide'ring mounted inside and'orr said body; a plurality. ofsguide rodsrjournaled.insaid guide rings, an L-ring and a c ringfixedlynmountedon said rodsand. having tuning portions to enter into and egress from saidrcavities whensaid guide rods are moved 1ongitudinally :and means connected to said rods for producing said longitudinal" motion to vary the tuning of said magnetron.

12f Ainagnetron of the type capable .of being continuously tuned through arange of frequencies comprisinga cylindricalsupporting body, a;

plurality of vanes positioned in a plane transverse to the center axis of the body and radially disposed about said axis, the size and spacing of said vanes forming together with said body a plurality of resonant cavities and determining substantially a mean frequency about which the frequency of said magnetron may be tuned, a plurality of guiding rings positioned on each side 01' said plane of vanes and mounted on said supporting body, a plurality of guide rods mounted freely in said guiding rings so that their free movement is permitted over a limited range, means in said resonators in the region at which a strong concentration of electric flux develops during operation for varying the capacitance of said resonators, means in said resonators in the region at which a strong concentration of electric flux develops during operation for varying the inductance of said resonators, said capacitance and inductance varying means being mounted on said guide rods, and means mounted between said supporting body and said guide rods for varying the position of said capacitance and inductance varying means relative to said resonators.

13. A magnetron according to claim 12 in which said plurality of guiding means comprise bearing surfaces through which said guide rods are journaled.

14. A vacuum device comprising an evacuated envelope, a plurality of elements mounted in a high temperature zone within said envelope, said elements being capable of relative motion one with respect to the other, and means also Within said envelope for constraining said motion between said elements comprising a tungsten rod extending through said zone and journaled on a copper bearing surface disposed outside said zone.

15. A vacuum device comprising an evacuated envelope, a plurality of elements mounted within said envelope, said elements being capable of relative motion one with respect to the other, and means for constraining said motion comprising a plurality of rods mounted in a substantially circular arrangement on one of said elements, said rods being journaled in bearings in another of said elements.

16. A vacuum tube assembly comprising a plurality of cavity resonators, reactance varying 10 elements for varying the frequency of said res onators, guiding means on which said elements are so mounted that they enter into or egress from said resonators, said guiding means comprising at least two journaled bearing surfaces, one mounted on each side of said plurality of cavity resonators.

17. A tunable magnetron comprising a metallic envelope, a plurality of cavity resonators mounted inside and on said envelope, a plunger adjustably mounted on said envelope at a position adjacent a predetermined region in said resonators for varying the resonant frequency thereof, and means mounted between said plunger and said envelope for making an electrical connection therebetween, said means comprising coiled springs arranged to be compressed sidewise in echelon fashion for making resilient connection therebetween whereby said plunger may be moved with respect to said envelope and said connection will be assured.

18. A tuning mechanism for a magnetron comprising a plurality of cavity resonators, plungers in regions of said resonators at which a strong concentration of magnetic flux develops during operation, further plungers in other regions of said resonators at which a strong concentration of electric flux develops during operation, said plungers being mounted on opposite sides of said resonators, and an adjustable member mechanically connected to said plungers for moving said plungers into and out of said resonators for simultaneously varying the inductance of said resonators at said first mentioned regions and the capacitance of said resonators at said other regions whereby the resonant frequency of said magnetron is varied.

CHARLES V. LITTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,078,672 Knowles Apr. 27, 1937 2,408,234 Spencer Sept. 24, 1946 2,422,465 Bondley June 17, 1947 

